Little bear harbouring isolated neutron star

A group of American and Canadian astronomers have spotted what appears to be an isolated neutron star relatively near to Earth, the BBC reports.

It is very rare for neutron stars to be found in singles: usually they have a companion supernova remnant for company. If it is confirmed, it will be only the eighth known lone neutron star ever found. As well as being odd because it is on its own, the star doesn't seem to be emitting any radio pulses, traditionally associated with neutron stars.

A neutron star is what is left after a massive star goes supernova. After the explosion throws off the star's outer layers, the remaining material continues to burn until the iron in the star's core ignites. Then it collapses under its own gravity, fusing protons and electrons to form neutrons. The remaining object may be no bigger than the average earth city, but will have a mass of roughly one and a half times that of our sun and a blazing internal temperature in the region of 100 million Kelvin.

The star, nicknamed Calvera, was first identified by Robert Rutledge of McGill University in Montreal, on a trawl through data from the German American Rosat satellite. He noticed an X-ray source that appeared in the Rosat data, and when he looked for it in other catalogues, he noticed there were no listings for the star in other wavelengths.

This prompted him to seek time on NASA's Swift satellite to pinpoint the location of the source. After that, follow up observations were made with the 8.1 metre Gemini North Telescope in Hawaii and NASA's Chandra X-ray Observatory.

The observations confirmed that the X-ray signal was not already associated with a known object. But it also left several puzzles for astronomers: how did the neutron star come to be where it is (high above the plane of our galaxy in the constellation Ursa Minor)? Why is it on its own? Why is there no visible signal associated with the star?

Professor Rutledge told the BBC: "Either Calvera is an unusual example of a known type of neutron star, or it is some new type of neutron star, the first of its kind." ®